Field of the Invention
The present invention relates to a gas filling method for filling gas in a tank.
Related Art
Fuel cell vehicles travel by supplying oxygenated air and hydrogen gas that is fuel gas to the fuel cell, and driving an electric motor using the electric power thereby generated. In recent years, progress has been made in the practical implementation of fuel cell vehicles employing such fuel cells as the energy source for generating motive power. Although hydrogen gas is required to generate electric power by fuel cells, with the fuel cell vehicles of recent years, vehicles have become mainstream that store a sufficient amount of hydrogen gas in advance in a high-pressure tank or a hydrogen tank equipped with a storage alloy, and use the hydrogen gas inside of the tank to travel. In concert with this, vigorous research has progressed also in the filling technology for quickly filling as much hydrogen gas as possible into the tank.
When hydrogen gas is filled in the tank, the pressure and temperature in the tank rise, and the rising state in the time has strong correlation mainly with a type, specifically, with a volume of the tank. Herein, a case where gas is filled in a general method, more specifically, a case where gas is filled while the pressure rise rate is maintained constant in a hydrogen station including a pre-cooling system that cools gas to be filled, is considered. In this case, the temperature rises gently during filling in a hydrogen tank having relatively large volume, while the temperature rises sharply during filling in a hydrogen tank having relatively small volume since such tank is easy to be influenced by a heat mass of a piping during filling. Therefore, in order to quickly fill hydrogen gas in a tank of a vehicle, a technique for acquiring a volume of a tank equipped in the vehicle as accurate as possible and rapidly, in a hydrogen gas supply side, i.e. a station side.
Non-Patent Document 1 illustrates a method for filling a small amount of hydrogen gas experimentally in a tank of which volume is unknown, and estimating the volume of the tank from variation of the state in the tank in the time. More specifically, the technology of Non-Patent Document 1 illustrates a method for estimating a volume of a tank by using the pressure rise width in the tank before and after a predetermined amount of hydrogen gas is filled. In this method, pressure is needed to be acquired before and after hydrogen gas is filled experimentally. Moreover, the fuel cell vehicles of recent years are equipped with sensors that detect the temperature and/or pressure in the tank. Therefore, when the estimation method of Non-Patent Document 1 is applied to the station to estimate the volume of the tank of the vehicle in the station side, the station utilizes communication with the vehicle to acquire the pressure rise width in the tank.
FIG. 15 is a view showing the magnitude and breakdown of the error of various types of sensors affecting on the volume estimation result, when the volume of the tank is estimated by known method by using the pressure rise width in the tank. In FIG. 15, the horizontal axis represents the pressure rise width in the tank (i.e. corresponding to the amount of experimentally filled hydrogen gas) and the vertical axis represents the absolute value of the error.
First, when the volume of the tank is estimated by the pressure rise width in the tank, as the above described method of Non-Patent Document 1, various sensors such as a mass flow meter that detects a mass flowrate of hydrogen gas (generally provided in the station), an ambient temperature sensor that detects the temperature of the atmosphere (generally provided in the station), and a pressure sensor arranged in a piping for detecting the pressure inside the tank (generally provided in the station). As illustrated in FIG. 15 with different patterns, the estimation result of the volume of the tank is influenced by the offset error of the mass flow meter, the offset error of the ambient temperature sensor, the offset error of the pressure sensor, and the pressure hysteresis error. Herein, the pressure hysteresis error is the error of the pressure sensor other than the offset error, the error generated by A/D conversion of output signals of the pressure sensor, and the error due to variation of valve opening pressure difference of check valves provided in the piping, or the like, and any of which has the hysteresis property in which a mark of the error cannot be predicted for every measurement time.
As illustrated in FIG. 15, among these four errors, the pressure hysteresis error affects the largest influence on the volume estimation result of the tank. In addition, the pressure hysteresis error is mostly inversely proportional to the pressure variation amount of the tank. This means that as the pressure rise width in the tank becomes larger, the volume in the tank can be estimated accurately. In other words, in order to estimate the volume of the tank accurately, it is preferable that the amount of hydrogen gas experimentally filled is increased as much as possible so that the pressure rise width in the tank is increased as much as possible.
Non-Patent Document 1: Shinichi Maruyama, “Volume estimation of FCV tank”, The 19th Fuel Cell Symposium proceedings, pp. 286-289